The present invention relates to thermally developable silver halide photothermographic materials.
Thermally developable silver halide photothermographic materials are disclosed in D. Morgan and B. Shely, U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. H. Klisterboer, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d in Imaging Processes and Materials, Neblette""s Eighth Edition, Edited by J. M. Sturge, V. Walworth and A. Shepp, page 2, 1989.
The thermally developable silver halide photothermographic material contains a reducible silver source (such as organic silver salts), a catalytic active amount of a photocatalyst (such as silver halide), a tone modifier controlling silver image tone and a reducing agent, which are usually in the form of being dispersed in organic binder. Silver halide photothermographic materials are stable at ordinary temperatures and when heated at a high temperature (e.g., 80xc2x0 C. or higher) after exposure, silver is formed through oxidation-reduction reaction between a reducible silver salt (which functions as an oxidizing agent) and a reducing agent. The oxidation-reduction reaction is catalyzed by latent images produced by exposure. Silver formed through reaction of an organic acid silver salt in exposed areas provides black-and-white images, which are in contrast to non-exposed areas. In the field of medical diagnostic and printing, advancements in the technique for processing are directed toward simplification, rapid access and friendliness to earth.
There is a system in this direction, including exposure to infrared laser (having wavelengths of 750 nm or more) and thermal processing. To obtain images with higher sharpness in this system, infrared dyes exhibiting absorption suited for infrared lasers are needed to prevent halation or irradiation. When a photosensitive layer is exposed to infrared rays, a part of the infrared rays which do not contribute to image formation penetrate to the support without being absorbed, is reflected thereon and returns to the image forming region, deteriorating sharpness of images. It is therefore necessary to absorb or shield as much as possible the infrared rays not contributing to image formation.
An antihalation layer to prevent halation is conventionally provided in any of the component layers of the photothermographic material, except for a sub-coating layer, specifically as a backing layer. However, it is impossible to completely prevent halation thereby. U.S. Pat. Nos. 4,581,323 and 4,312,941 disclose such a layer to prevent composite reflection of light scattered between layers internal to the photosensitive component. U.S. Pat. Nos. 4,477,562 and 4,409,316 disclose a peelable antihalation layer by the use of carbon black. In this method, however, the peelable layer makes difficult adhesion thereto during the stage of coating, converting or packaging and also produces colored scrap sheets. Therefore, these techniques are not desirable methods to solve the problems described above.
After being subjected to exposure and thermal processing, the photothermographic material sometimes produces nonuniformity due to interference fringes. It is contemplated that this nonuniformity due to interference fringes originates before formation of the images, i.e., at the stage of preparing the photothermographic material and its influence is displayed at the time of exposure. It is therefore desired to solve such problems.
U.S. Pat. No. 4,581,325 and European Patent 377,961 disclose photothermographic material containing polymethine and nonpolar dyes to prevent infrared halation. These dyes exhibit not only superior infrared absorptivity but also visible light absorptivity in the subsequent exposure.
JP-A 7-191432 (hereinafter, the term, JP-A means an unexamined and published Japanese Patent Application) discloses incorporation of water-soluble polymethine dyes in a hydrophilic layer of a silver halide photothermographic material. U.S. Pat. No. 5,496,695 and Tokuhyohei 9-509503 discloses squarylium dyes exhibiting no absorption in the visible region; and JP-A 7-191432 and 9-230531 disclose infrared absorbing polymethine dyes.
To solve problems described above, such as deterioration in Image sharpness and uneven density due to interference fringes produced when silver halide photothermographic materials are exposed to infrared rays to form images, the following techniques were disclosed.
The use of the squarylium dyes and polymethine dyes described above was found to be effective to some extents to prevent halation. However, incorporation of the dyes into an antihalation layer or a photosensitive layer thickens fine image portions, easily deteriorating sharpness.
JP-B 6-10735 and JP-A 8-211521 discloses methods for improving interference fringes. However, satisfactory results were not obtained. Further, it was found that when infrared absorbing compounds such as infrared dyes were used in the backing layer, remarkable interference fringes were often observed.
Accordingly, an object of the present invention is to provide silver halide photothermographic materials exhibiting antihalation effects, superior sharpness and with no uneven density due to interference fringes.
The object of the present invention can be accomplished by the following constitution:
1. A silver halide photothermographic material comprising on a support an organic silver salt and a silver halide, wherein the support has thereon a sublayer containing an infrared absorbing compound exhibiting an absorption maximum at a wavelength of 700 to 900 nm;
2. The photothermographic material described in 1., wherein the infrared absorbing compound is a water-soluble infrared absorbing compound, a compound represented by formula (I), a compound represented by formula (II), a copper-containing phosphate compound or metal oxide particles:
formula (I) 
xe2x80x83wherein Z1 and Z2 are each a nonmetallic atom group necessary to complete a 5- or 6-membered nitrogen-containing ring; R1 and R2 are each an alkyl group, an alkenyl group, or an aralkyl group; L is a linkage group, in which 5, 7 or 9 methine groups are linked with each other through conjugated double bonds; a, b and c are each 0 or 1; and Xxe2x88x92 is an anion;
formula (II) 
xe2x80x83wherein R1, R4, R5 and R8 are each a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl or aralkyl group; R2, R3, R6 and R7 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, an aryl group. a heterocyclic group or an aralkyl group, xe2x80x94CH2OR, in which R is an alkylacyl group, xe2x80x94C(xe2x95x90O)Rxe2x80x2, xe2x80x94SiRxe2x80x3Rxe2x80x2xe2x80x3Rxe2x80x3xe2x80x3 or xe2x80x94SO2Rxe2x80x2xe2x80x3xe2x80x3, in which Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x2xe2x80x3xe2x80x3 are each an alkyl group, or R1 and R2, R3 and R4, R5 and R6, R7 and R8, or R2 and R3, or R6 and R7 combine together with each other to form a 5-, 6- or 7-membered ring; R9 and R10 are each a univalent group; and n is an integer of 1 to 3;
3. The photothermographic material described in 1., wherein the infrared absorbing compound is a water-soluble infrared absorbing compound;
4. The photothermographic material described in 1., wherein the infrared absorbing compound is a compound represented by formula (I):
formula (I) 
xe2x80x83wherein Z1 and Z2 are each a nonmetallic atom group necessary to complete a 5- or 6-membered nitrogen-containing ring; R1 and R2 are each an alkyl group, an alkenyl group, or an aralkyl group; L is a linkage group, in which 5, 7 or 9 methine groups are linked with each other through conjugated double bonds; a, b and c are each 0 or 1; and Xxe2x88x92 is an anion;
5. The photothermographic material described in 1., wherein the infrared absorbing compound is a compound represented by formula (II):
formula (II) 
xe2x80x83wherein R1, R4, R5 and R8 are each a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl or aralkyl group; R2, R3, R6 and R7 are each a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, a heterocyclic group or an aralkyl group, xe2x80x94CH2OR, in which R is an alkylacyl group, xe2x80x94C(xe2x95x90O)Rxe2x80x2, xe2x80x94SiRxe2x80x3Rxe2x80x2xe2x80x3Rxe2x80x3xe2x80x3 or xe2x80x94SO2Rxe2x80x2xe2x80x3xe2x80x3, in which Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x2xe2x80x3xe2x80x3 are each an alkyl group, provided that R1 and R2, R3 and R4, R5 and R6, R7 and R8, or R2 and R3, or R6 and R7 may combine together with each other to form a 5-, 6- or 7-membered ring; R9 and R10 are each a univalent group; and n is an integer of 1, 2 or 3;
6. The photothermographic material described in 1., wherein the infrared absorbing compound is contained in an amount of 0.1 to 1000 mg/m2;
7. The photothermographic material described in 1., wherein the infrared absorbing compound is a copper-containing phosphate compound;
8. The photothermographic material described in 4., wherein the infrared absorbing compound is a compound represented by formula (I-1) or (I-2):
formula (I-1) 
xe2x80x83wherein Z3 and Z4 are each the group of atoms necessary to form a fused benzo- or naphtha-ring; R13 and R14 are each an alkyl group, an aralkyl group or alkenyl group; R19 and R21 are each the group of atoms necessary to form a 5- or 6-membered ring by combining with each other; R20 is a hydrogen atom, an alkyl group, a halogen atom, an aryl group, NR22R23, SR24 or OR24, in which R22, R23 and R24 are each an alkyl group or aryl group, provided that R22 and R23 may combine with each other to form a 5- or 6-membered ring; R15, R16, R17 and R18 are each an alkyl group, provided that R15 and R16, or R17 and R18 combine with each other to form a ring; Xxe2x88x92 is an anion; and c is 0 or 1; 
xe2x80x83wherein Z3 and Z4 are each the group of atoms necessary to form a fused benzo- or naphtho-ring; R13 and R14 are each an alkyl group, an aralkyl group or alkenyl group; R22 and R23 are each an alkyl group or an aryl group; R15, R16, R17 and R18 are each an alkyl group, provided that R15 and R16, or R17 and R18 may combine with each other to form a 5- or 6-membered ring; Xxe2x88x92 is an anion and c is 0 or 1;
9. The photothermographic material described in 4., wherein the infrared absorbing compound is a copper-containing phosphate compound exhibiting a molar ratio of copper as calculated in terms of CuO to phosphate in terms of P2O5, CuO/P2O5 of 0.05 to 4;
10. The photothermographic material described in 1., wherein a layer containing said infrared absorbing compound is between the support and an emulsion layer and adjacent to the emulsion layer;
11. The photothermographic material described in 5., wherein in the formula, R1, R4, R5 and R8 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or an aryl having not more than 14 carbon atoms or aralkyl group; R2, R3, R6 and R7 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl having not more than 14 carbon atoms, a heterocyclic group or an aralkyl group, xe2x80x94CH2OR, in which R is an alkylacyl group, xe2x80x94C(xe2x95x90O)Rxe2x80x2, xe2x80x94SiRxe2x80x3Rxe2x80x2xe2x80x3Rxe2x80x3xe2x80x3 or xe2x80x94SO2Rxe2x80x2xe2x80x3xe2x80x3, in which Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3 Rxe2x80x3xe2x80x3 and Rxe2x80x2xe2x80x3xe2x80x3 are each an alkyl group having 1 to 20 carbon atoms, or R1 and R2, R3 and R4, R5 and R6, R7 and R8, or R2 and R3, or R6 and R7 combine together with each other to form a 5-, 6- or 7-membered ring; R9 and R10 are each a univalent group; and n is an integer of 1 to 3, with proviso that when R2, R3, R6 and R7 are each a heterocyclic group, R9 and R10 may be a hydrogen atom;
12. The photothermographic material described in 5., wherein said infrared absorbing compound is a compound represented by formula (III), (IV) or (V):
formula (III) 
xe2x80x83wherein R11, R14, R15 and R18 are each a hydrogen atom, an alkyl group, a cycloalkyl group, or an aryl or aralkyl group; R12, R13, R16 and R17 are hydrogen atom, alkyl a cycloalkyl group, an aryl group, a heterocyclic group, an aralkyl group, xe2x80x94CH2OR, in which R is an alkylacyl group, xe2x80x94C(xe2x95x90O)Rxe2x80x2, xe2x80x94SiRxe2x80x3Rxe2x80x2xe2x80x3Rxe2x80x3xe2x80x3, or xe2x80x94SO2Rxe2x80x2xe2x80x3xe2x80x3 in which Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x2xe2x80x3xe2x80x3 are each an alkyl group, provided that R11 and R12, R13 and R14, R15 and R16, R17 and R18, R12 and R13, or R16 and R17 may combine with each other to form a 5-, 6- or 7-membered ring; R19 and R are each a univalent group; and n is an integer of 1, 2 or 3;
formula (IV) 
xe2x80x83wherein R21, R24, R25, and R28 are each a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, R22, R23, R26 and R27 are each a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, a heterocyclic group or an aralkyl group, provided that R21 and R22, R23 and R24, R25 and R26, R27 and R28, R22 and R23, or R26 and R27 may combine with each other to form a 5- or 6-membered ring; R29 and R30 are each a hydrogen atom or a univalent group; n is an integer of 1, 2 or 3; and
formula (V) 
xe2x80x83wherein R31, R34, R35 and R38 are each a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, R32, R33, R36 and R37 are each a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, a heterocyclic group or an aralkyl group, provided that R31 and R32, R33 and R34, R35 and R36, R37 and R38, R32 and R33, or R36 and R37 may combine with each other to form a 5- or 6-membered ring; R39 and R40 are each a hydrogen atom or a univalent group; and n is an integer of 1, 2 or 3;
13. The photothermographic material described in 1., wherein the sublayer contains a binder, the binder being comprised of at least two kinds of polymers and the difference in glass transition temperature between the two kinds of polymers is 10 to 80xc2x0 C.;
14. The photothermographic material described in 10., wherein the infrared absorbing compound is a compound represented by formula (I), in an amount of 0.1 to 1000 mg/m2:
formula (I) 
xe2x80x83wherein Z1 and Z2 are each a nonmetallic atom group necessary to complete a 5- or 6-membered nitrogen-containing ring; R1 and R2 are each an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms; L is a linkage group, in which 5, 7 or 9 methine groups are linked with each other through conjugated double bonds; a, b and c are each 0 or 1; and X is an anion;
15. The photothermographic material described in 10., wherein said infrared absorbing compound is a compound represented by formula (II), in an amount of 0.1 to 1000 mg/m2:
formula (II) 
xe2x80x83wherein R1, R4, R5 and R8 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or an aryl having not more than 14 carbon atoms or aralkyl group; R2, R3, R6 and R7 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl having not more than 14 carbon atoms, a heterocyclic group or an aralkyl group, xe2x80x94CH2OR, in which R is an alkylacyl group, xe2x80x94C(xe2x95x90O)Rxe2x80x2, xe2x80x94SiRxe2x80x3Rxe2x80x2xe2x80x3Rxe2x80x3xe2x80x3 or xe2x80x94SO2Rxe2x80x2xe2x80x3xe2x80x3, in which Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x2xe2x80x3xe2x80x3 are each an alkyl group having 1 to 20 carbon atoms, provided that R1 and R2, R3 and R4, R5 and R6, R7 and R8 , or R2 and R3, or R6 and R7 may combine together with each other to form a 5-, 6- or 7-membered ring; R9 and R10 are each a univalent group; and n is an integer of 1, 2 or 3;
16. The photothermographic material described in 15., wherein the infrared absorbing compound is a compound represented by formula (III), (IV) or (V):
formula (III) 
xe2x80x83wherein R11, R14, R15 and R18 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or an aryl having not more than 14 carbon atoms or aralkyl group; R12, R13, R16 and R17 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having not more than 14 carbon atoms, a heterocyclic group, an aralkyl group, xe2x80x94CH2OR, in which R is an alkylacyl group, xe2x80x94C(xe2x95x90O)Rxe2x80x2, xe2x80x94SiRxe2x80x3Rxe2x80x2xe2x80x3Rxe2x80x3xe2x80x3, or xe2x80x94SO2Rxe2x80x2xe2x80x3xe2x80x3 in which Rxe2x80x2, Rxe2x80x3, Rxe2x80x2xe2x80x3, Rxe2x80x3xe2x80x3 and Rxe2x80x2xe2x80x3xe2x80x3 are each an alkyl group having 1 to 20 carbon atoms, provided that R11 and R12, R13 and R14, R15 and R16, R17 and R18, R12 and R13, or R16 and R17 may combine with each other to form a 5-, 6- or 7-membered ring; R19 and R20 are each a univalent group; and n is an integer of 1, 2 or 3;
formula (IV) 
xe2x80x83wherein R21, R24, R25 and R28 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having not more than 14 carbon atoms, or an aralkyl group, R22, R23, R26 and R27 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having not more than 14 carbon atoms, a heterocyclic group or an aralkyl group, provided that R21 and R22, R23 and R24, R25 and R26, R27 and R28, R22 and R23, or R26 and R27 may combine with each other to form a 5- or 6-membered ring; R29 and R30 are each a hydrogen atom or a univalent group; n is an integer of 1, 2 or 3; and
formula (V) 
xe2x80x83wherein R31, R34, R35 and R38 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having not more than 41 carbon atoms or an aralkyl group, R32, R33, R36 and R37 are each a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having not more than 41 carbon atoms, a heterocyclic group or an aralkyl group, provided that R31 and R32, R33 and R34, R35 and R36, R37 and R38, R32 and R33, or R36 and R37 may combine with each other to form a 5- or 6-membered ring; R39 and R40 are each a hydrogen atom or a univalent group; and n is an integer of 1, 2 or 3.